1. Field of the Invention
The present invention relates to apparatus for controlling the flow of plastic materials from an injection molding machine to an injection mold cavity. More particularly, the present invention relates to an improved valve gate for use in an injection molding machine, wherein the valve gate incorporates an actuator for positively operating an elongated valve pin between valve open and valve closed positions.
2. Description of the Related Art
To control flow of heated, fluent plastic material from an injection molding machine into a mold, a flow control valve is normally provided at some point between the outlet end of the barrel of the machine's injection unit and the mold cavity. Such valves, sometimes referred to as "valve gates," include a generally tubular valve body containing an elongated valve pin. The valve pin end is adapted to engage a mating valve seat at the interior of one end of the valve body to open and close an outlet opening selectively. The valve pin is moved in to or out of engagement with the valve seat by a suitable actuator.
One form of known valve and valve actuator for controlling the injection of plastic melt into a mold cavity is disclosed in U.S. Pat. No. 4,449,915, entitled "Closure System for Fluent Injection Apparatuses," issued on May 22, 1984. That patent describes a valve actuator that includes a rotary cam plate having a pair of spaced, so-called pressure areas that are each radially offset from a cam plate pivot axis. One of the pressure areas receives a cross pin that is connected with an elongated valve pin, and the other pressure area receives a cross pin of a fluid-operated actuator. Operation of the fluid actuator causes the actuator cross pin to cause the cam plate to rotate about its pivot axis, causing movement of the valve pin cross pin, and the valve pin, toward or away from a discharge opening. However, actuator structures of this type are prone to pivot breakage, and also impose undesirable side loads on the valve pin, thereby causing excessive wear.
Another form of valve actuator for a flow control valve associated with a mold in an injection molding machine is shown in U.S. Pat. No. 4,095,931, entitled "Injection Molding Machine and Method," issued on Jun. 20, 1978. The actuator shown in this patent includes a transversely mounted and transversely movable rod having a reduced diameter portion that defines a cam surface for engaging the end of a shut-off pin. This type of actuation also imposes undesirable side loads on the shutoff pin resulting in high wear along the line of contact.
Another known valve actuator for controlling the flow of fluent molding material is disclosed in U.S. Pat. No. 5,067,893, entitled "Injection Molding Apparatus with Shut Off Valve Pin Actuation System," issued on Nov. 26, 1991. The actuator shown in that patent includes a rack and pinion arrangement for shifting a valve pin between open and closed positions. The rack is provided adjacent the end of the valve pin that is spaced from the outlet opening, and the pin is moved in an axial direction by a pinion that is in engagement with the rack and that is rotated by a suitable actuation cylinder that operates through a right-angle drive. Such a valve pin drive arrangement has been found to involve excessive gear and rack tooth wear over time, along with difficulties in positively supporting the valve pin, which can result in undesirable side loads on the valve pin.